Taiwanese Patent Publication No. 474237 discloses an illuminative device 30 of a socket wrench. The socket includes a socket 10 in which the illuminative device 30 is installed. The illuminative device 30 includes a light 31 and two batteries 38. The socket 10 defines a square hole 11 in an end and a hexangular hole 12 in an opposite end. The square hole 11 is for receiving a square insert 51 of the handle 50. The hexangular hole 12 is for receiving a hexangular insert of a selective one of several joints 20, 21 and 22. Each of the joints 20, 21 and 22 can be connected with sockets (not shown) for engagement with bolts. Each of the joints 20, 21 and 22 defines a hole 203 through which light can pass. This structure however does not fit in open-ended wrenches. Moreover, the light 31 is not turned on until the square insert 51 is inserted in the square hole 11, i.e., the illuminative device 30 only works dependently.
The present invention is therefore intended to obviate or at least alleviate the problems encountered in the prior art.